There have been known storage containers for medical use for storing liquid (blood, etc.) sucked out from the thoracic cavity together with gas that has leaked from the lungs to the thoracic cavity of a patient. For example, Japanese Unexamined Patent Publication No. H07-213599 discloses a storage container including a liquid collecting section including a storage space for storing liquid, a suction-pressure setting section including a suction space connected to a suction pump, and a water sealing section provided between the liquid collecting section and the suction-pressure setting section. In the liquid collecting section, an inflow port for causing liquid and gas in the body cavity of the patient to flow into the liquid collecting section via a tube inserted into the body cavity is provided. The pressure in the suction space is adjusted according to an injection amount of sterile water into the suction-pressure setting section. In an upper part of the suction-pressure setting section, an opening for taking air on the outside into the suction-pressure setting section is provided. The air flows into the suction-pressure setting section through the opening, whereby the pressure in the suction space is maintained constant. The water sealing section is capable of sealing the storage space and the suction space off from each other with the sterile water. The water sealing section is provided for the purpose of, for example, preventing counterflow of outside air into the patient through the suction space and the storage space when the pressure in the storage space drops below the pressure in the suction space.
When the suction pump is driven in a state in which the tube has been inserted into the body cavity of the patient, the liquid and the gas in the body cavity of the patient flow into the liquid collecting section via the inflow port. The liquid that has flowed into the liquid collecting section is stored in a bottom section of the liquid collecting section. On the other hand, the gas that has flowed into the liquid collecting section changes to air bubbles and passes through the sterile water in the water sealing section and is thereafter discharged from the storage container through the suction space.
In a case where the liquid and the gas in the body cavity are sucked using the storage container, if a large amount of gas, i.e. equal to or more than an amount of gas in a steady state, temporarily flows into the liquid collecting section because, for example, the patient coughs, a state of the liquid collecting section changes to an excessive positive pressure state. In the excessive positive pressure state, it is difficult for the patient to inflate the lungs (breathe). Therefore, a positive-pressure relief valve for avoiding the excessive positive pressure state is provided in the liquid collecting section of the storage container. That is, when a large amount of gas temporarily flows into the liquid collecting section, the positive-pressure relief valve opens, whereby excess gas is discharged from the storage space to the outside of the storage container. As a result, although the state of the liquid collecting section is suppressed from changing to the excessive positive pressure state, since a total amount of the gas in the body cavity or the liquid collecting section decreases, the state of the liquid collecting section changes to an excessive negative pressure state according to subsequent breathing of the patient. In the excessive negative pressure state, a large load is applied to the lungs. Therefore, in the storage container, a one-way valve for avoiding the excessive negative pressure state of the liquid collecting section is provided. The one-way valve is provided in a partition wall in the water sealing section, which wall defines the storage space and the suction space. The one-way valve allows only passage of the gas from the suction space to the storage space. That is, after the gas is discharged from the liquid collecting section to the outside via the positive-pressure relief valve, the one-way valve opens when the pressure of the liquid collecting section drops according to the breathing of the patient, and as a consequence, the gas flows into the liquid collecting section, whereby the state of the liquid collecting section is suppressed from changing to the excessive negative pressure state.
In the storage container described in Japanese Unexamined Patent Publication No. H07-213599, the inside of the liquid collecting section (the storage space) communicates with the outside air while the positive-pressure relief valve is open and while the one-way valve is open. Therefore, infection may occur between the patient and other people. Specifically, while the positive-pressure relief valve is open, the gas in the storage space, that is, the gas in the body cavity of the patient is discharged to the outside, and therefore, if a pathogen is included in the gas, infection to people other than the patient may occur. On the other hand, while the one-way valve is open, the outside air directly flows into the storage space through the one-way valve without passing through the sterile water in the water sealing section, and therefore, if a pathogen is included in the outside air, infection to the patient may occur.